Scattering Effect on Anomalous Hall Effect in Ferromagnetic Transition Metals

Abstract

The anomalous Hall effect (AHE) has been discovered for over a century, but its origin is still highly controversial theoretically and experimentally. In this study, we investigated the scattering effect on the AHE for both exploring the underlying physics and technical applications. We prepared Cox(MgO)100-x granular thin films with different Co volume fraction (34≤𝑥≤100) and studied the interfacial scattering effect on the AHE. The STEM HAADF images confirmed the inhomogeneous granular structure of the samples. As 𝑥 decreases from 100 to 34, the values of longitudinal resistivity (𝜌𝑥𝑥) and anomalous Hall resistivity (𝜌AHE) respectively increase by about four and three orders in magnitude. The linear scaling relation between the anomalous Hall coefficient (𝑅𝑠) and the 𝜌𝑥𝑥 measured at 5 K holds in both the as-prepared and annealed samples, which suggests a skew scattering dominated mechanism in Cox(MgO)100-x granular thin films. We prepared (Fe36/𝑛/Au12/𝑛)𝑛, (Ni36/𝑛/Au12/𝑛)𝑛 and (Ta12/𝑛/Fe36/𝑛)𝑛 multilayers to study the interfacial scattering effect on the AHE. The multilayer structures were characterized by the XRR spectra and TEM images of cross-sections. For the three serials of multilayers, both the 𝜌𝑥𝑥 and 𝜌AHE increase with 𝑛, which clearly shows interfacial scattering effect. The intrinsic contribution decreases with 𝑛 increases in the three serials of samples, which may be due to the crystallinity decaying or the finite size effect. In the (Fe36/𝑛/Au12/𝑛)𝑛 samples, the side-jump contribution increases with 𝑛𝑛, which suggests an interfacial scattering-enhanced side jump. In the (Ni36/𝑛/Au12/𝑛)𝑛 samples, the side-jump contribution decreases with 𝑛 increases, which could be explained by the opposite sign of the interfacial scattering and grain boundary scattering contributed side jump. In the (Ta12/𝑛/Fe36/𝑛)𝑛 multilayers, the side-jump contribution changed from negative to positive, which is also because of the opposite sign of the interfacial scattering and grain boundary scattering contributed side jump. The interfacial scattering effect on the AHE is much more complicated than surface scattering in thin films or scattering by delta-impurities in bulk-like samples.